1. Field of the Invention
The present invention relates to inspecting devices, and more particularly, to a readily transportable, detachable device that is adapted for viewing and photographing the cavities or interiors of elongated hollow articles such as rocket motors and the like.
2. Description of the Prior Art
In solid propellant rocket motors, the charge of propellant is cast in the rocket motor casing and cured. Typically, the propellant is cast with the internal surface of the hollow bore or cavity having a predetermined configuration, such as that of a star, with alternating star valleys and star points.
The interior surface of a rocket motor solid propellant charge is designed to produce the quantity of gas required for creating the desired operating pressure of the motor. Surface irregularities or defects such as cracks, lumps, etc. in the interior surface of the cavity of the propellant increase the burning area. This causes an undesirable increase in the internal pressure that could result in the destruction of the motor.
Accordingly, after the charge of propellant has been cast and cured, and before the motor is stored, it is very desirable and important to inspect the interior for defects. Additionally, since aging may adversely affect the interior surface of the propellant charge, periodic inspection thereof during storage of the rocket motor also is important.
Devices for inspecting the interior surface of a rocket motor cast propellant charge have been proposed in the prior art. Typical of such proposals are the disclosures of U.S. Pat. Nos. 3,329,059, granted on July 4, 1967 to J. McCormac, and of 3,382,757 granted on May 4, 1968 to J. A. Poirrier. Both of these patents are assigned to Thiokol Corporation, the assignee of the present invention.
The inspecting device of U.S. Pat. No. 3,329,059 includes a long thin-walled, relatively large diameter tubular housing that extends for substantially the entire length of the propellant body, coincident with the central axis of the rocket motor. At the viewing end thereof, the tubular housing is supported by an adapter that is connected to the igniter opening at the head end of the rocket motor. At the other end, the tubular housing is supported by a plurality of spring loaded pivotable support arms that pivot radially outwardly to engage star points on the interior surface of the propellant. Bearing means provided at each end of the tubular housing allow the latter to be rotated through 360.degree. with respect to the support arms.
A longitudinal slot extends along one side of the housing for substantially the entire length. Two longitudinally spaced and independently adjustable rectangular reflectors that are actuable longitudinally of the propellant bore by a sprocket and tape system are arranged to reflect light through the slot to the interior surface of the propellant from a housed light source that is provided exteriorly of the motor, at the viewing end of the tubular housing. The reflectors are both angularly adjustable relatively to the axis of the tubular housing, the reflector closer to the light source being narrower than the other one so as not to obstruct all of the light to the latter. The viewing means comprises a telescope that extends into the end of the tubular housing at the outside of the motor.
In operation, the inspecting device is inserted into the propellant cavity through the igniter opening in the head end of the rocket motor. As inserted, the plurality of support arms are pivoted so that they lie parallel to the central axis of the tubular housing. Upon insertion into the hollow bore of the cast propellant, the support arms pivot radially outward by spring action to effect contact of rollers on the ends thereof with propellant star points thereby to align the tubular housing with the central axis of the latter.
In another embodiment disclosed in U.S. Pat. No. 3,329,059, the tubular housing is greatly reduced in length, and supports only the light source and the telescope. The need for rotating the housing is eliminated, and the angles of the reflectors are not adjustable relatively to the axis of the inspecting device. A long frame, centered on the central axis of the cast propellant and extending the length of the cavity, is supported in a manner similar to that of the first described embodiment. The frame supports two longitudinally spaced and relatively movable conical reflectors, the reflectors being adapted for sliding longitudinal movement along the frame relative to each other and to the observer at the telescope. A pulley system is provided for sliding the conical reflectors longitudinally of the bore of the cast propellant.
The inspecting device of U.S. Pat. No. 3,382,757 includes a wheeled carriage for traversing the hollow bore or cavity to be inspected. The wheels of the carriage are biased to ride in star valleys at opposite sides of the propellant, thus suspending the carriage between them. A sectional control rod is provided for moving the carriage. The control rod is extensible exteriorly of the rocket motor, from the head end thereof, and is rotatable for adjusting a transmission housing on the carriage. A cantilevered beam, extending from the transmission housing and positioned adjacent the control rod, supports internally of the bore under inspection two appropriately positioned light sources and an angled mirror. The mirror is attached to the end of the beam facing the head end of the motor. A telescope, separately mounted on the motor at the head end thereof, is sighted on the mirror and provides a view of a portion of the interior surface of the propellant by means of longitudinal and rotational adjustment of the control rod from outside the motor.
Such prior art inspection systems are characterized by a number of inherent disadvantages. They are overly complicated, involve many parts, are bulky and cumbersome, and do not lend themselves to being transported readily by automobile or aircraft. Additionally, since the supporting means for the inspection devices, internally of the motor, are positioned further from the viewing means than the reflectors, such inspection devices do not readily allow an inspection of the entire propellant cavity surface. Thus, there exists a need and a demand in the art for further improvements in devices for the inspection of the interior of solid propellant rocket motors or similar articles.